Billy helps to combat the symptoms by going to the gym four times a week and doing crosswords to keep his mind sharp.

He keeps a notebook listing “all the words I tend to forget”. He said: “It’s the same ones cropping up again and again.”

Having cancer or Parkinson’s has not stopped Billy from working.

In the new documentary, he visits the Necropolis in Glasgow and pops over to California to look at unusual burials.

Viewers will see him introduced to an eco death suit threaded with mushroom spores which turns the body into compost.

Speaking about his own demise, Billy said: “I don’t think I want a resting place. I want to be scattered to the wind.”

But he has not made up his mind. In a Radio Times interview, the star said he would like to have a public funeral with an empty coffin while he is “being buried somewhere by pals, quietly, with a tree on top of me”.

Billy’s close friend Eric Idle also shares his thoughts on funerals for the documentary.

The Monty Python star said he would like fireworks during his final farewell.

Billy joked that he would go further to create a party atmosphere by giving drugs to the mourners.

He said: “I’m paying for drugs for mine, because I’ve heard they’re very popular too.”

Billy, who has lived in New York with Pamela for eight years, is currently on tour.

He will be in the UK in the autumn but will be visiting New Zealand when the independence referendum is held on September 18 and will not vote on Scotland’s future. He has deliberately refused to be drawn into the independence debate, saying it’s for the people of Scotland to make up their own minds.

But Billy added: “I don’t believe in having more layers of government that ordinary people will have to pay for.

“It’s time for people to get together, not split apart. The more people stay together, the happier they’ll be.

“I don’t have great belief in the Union of England and Scotland. But I have a great belief in the union of the human race.”

While he won’t commit to taking sides in the referendum, Billy does have a few bugbears to air.

He added: “I’m really tired of people saying England won the war and calling Britain England. But you must remember that the Union saved Scotland.

“Scotland was bankrupt and the English opened us up to their American and Canadian markets, from which we just flowered.

“I dislike patriots. I’m deeply suspicious of patriotism, people following the band, you know?

“I don’t want to be part of it. It’s paved with fools.”

* BILLY Connolly’s Big Send Off starts on STV on Wednesday, May 7 at 9pm. Parts of this interview are from this week’s Radio Times, out now.